One thing to check before replacing your heater blower motor is that it’s really broken. I discovered, after a period of non-use, that the friction in the bearings can be greater that the torque developed in the windings and mine wouldn’t tum. Since it can’t move, the wires get hot and, at best, a fuse blows. A smoldering fire is not unheard of.
If your blower isn’t working. remove the deflector assembly and associated works under the dash and remove the three main mounting bolts. Rotate the blower assembly out of the large rubber adapter and tum the squirrel-cage blade. Spin it once or twice and then apply power. If it starts up, it’s not burned out, just stuck.
The lower bearing is inaccessible without disassembling the entire motor, but it’s possible to lubricate the upper bearing if you use a long, pointed applicator and 10W oil. Keep oil away from the plastic squirrel-cage, as British plastic, like their rubber, may self-destruct. Run the fan to work oil into the bearing and exercise it regularly to keep it running.